This invention relates to the purification of air-borne particulates and gasses, in particular volatile organic compounds.
It has been known for some time that titanium dioxide can achieve photodechlorination of PCB""S, as described by J. H. Carey et al in xe2x80x9cPhotodechlorination of PCB""s in the Presence of Titanium Dioxide in Aqueous Suspensions,xe2x80x9d xe2x80x9cBulletin of Environmental Contamination and Toxicology,xe2x80x9d Vol. 16, No. 6, pp. 697-701, 1976 Springer-Verlag New York Inc. Carey et al describe irradiation by ultra violet light with a wavelength of 365 nm of a 25 ppb aqueous solution of Aroclor 1254 in the presence of suspended particulate titanium dioxide. After 30 minutes no unreacted Aroclor could be detected in solution or adsorbed on the surface of the TiO2. Similar experiments were conducted with other PCB""s and resulted in an observed disappearance of the chlorinated biphenyls and the production of chloride ions. It has been reported the conversion (often called xe2x80x9cmineralizationxe2x80x9d) of a number of organic compounds to carbon dioxide by exposure to near ultra violet light in aqueous suspensions of anatase, a form of crystalline titanium dioxide. The solutes studied were benzene, benzoic acid, benzoate ion, salicylate ion, phenol, chlorobenzene, aniline, anilinium ion, nitrobenzene, chloroform and formic acid. Also it had been earlier reported that similar results with benzoic acid or sodium benzoate (xe2x80x9cHydroxylation Reactions Induced by Near-Ultraviolet Photolysis of Aqueous Titanium Dioxide Suspensions,xe2x80x9d J. Chem. Soc. Faraday Trans. 1, 1984, 80, pp 457-471).
Chen-Yung Hsiao et al. have also reported the mineralization of chloromethanes to CO2 and HCl by the heterogeneous photocatalyst TiO2 (xe2x80x9cHeterogeneous Photocatalysis: Degradation of Dilute Solutions of Dichloromethane (CH2 Cl2), Chloroform (CHCl3), and Carbon Tetrachloride (CCl4) with Illuminated TiO2 Photocatalyst,xe2x80x9d Journal of Catalysis 82, 1983, pp 418-423). Similar reactions have not been limited to TiO2. Other metal semiconductors, such as ZnO, CdS, WO3 and SnO2, have been utilized in photocatalytic processes for the degradation of environmental contaminants (xe2x80x9cPhotocatalysis Over TiO2 Supported On A Glass Substrate,xe2x80x9d by N. Serpone et al, Solar Energy Materials 14(1986) pp 121-127, Elsevier Science Publishers B.V.-North-Holland Physics Publishing Divisions, Amsterdam).
Robertson et al. in U.S. Pat. No. 4,966,759 disclose and claim a matrix for use in a method of removing, reducing or detoxifying organic pollutants from a fluid. The matrix is a substrate in the form of a plurality of layers of a filamentous, fibrous or stranded base material, and a photoreactive metal semiconductor material bonded with, to or into surfaces of the layers. And at least one of the layers being at least partially transparent to light at a wavelength to which the semiconductor material photoreacts. The filamentous, fibrous or stranded base material disclosed by Robertson et al. are fiberglass, glass wool, and steel.
The filamentous, fibrous or stranded base materials of glass wool and fiberglass, as found by the present applicant, were unable to withstand extended periods in ultraviolet light without altering the adherence of the anatase to the base material. Similarly, steel is unable to withstand extended periods of exposure to hydroxyl compounds without rusting. Also, these base materials are not water absorbent because an object of Robertson et al.""s invention was to use a base material for the water to flow through or on it, not be trapped within. (First paragraph of the Detailed Description of the Invention.) Hence, water is not trapped in the material, which is an embodiment of the present invention in order to upon reaction with UV light and anatase form hydroxyl radicals, which create undesirable effect on the steel substrate which is discussed above.
The present invention solves these problems of the prior art. This invention is an air purifying matrix to remove, reduce or detoxify organic pollutants. The matrix has an inert substrate, a photoreactive semiconductor material, and aqueous particles. The inert substrate is water absorbent, transparent to ultraviolet light, able to withstand extended periods of exposure to all wavelengths of ultraviolet light side of the spectrum without decomposing or altering the structure thereof, able to withstand high concentrations of hydroxyl radicals without decomposing or altering the structure thereof, and in the form of an expanded granular type with spaces therein. The photoreactive semiconductor material is crystallized within the spaces. And the aqueous particles are within the spaces to form photoreactive metal semiconductor material nano-reactors within the matrix. These nano-reactors generate high concentrations of hydroxyl radicals which surround and diffuse through the matrix, and remove, reduce or detoxify organic pollutants within and surrounding the matrix. Moreover, the ultraviolet light is at a wavelength which the semiconductor material photoreacts.